Forest landscapes, especially flysch zones are impacted by considerable deforestation due to large scale commercial forestry activity and development. Timber harvesting with heavy machinery has created a large number of approach roads not only in sloping terrain but also in and along streams. In the case of Slovakia, growth in timber harvesting is not accompanied by adequate construction of suitable forestry roads, as such retrieving timber from forests is accompanied by the formation of large erosion gullies and increased destruction of the natural eco-system. These erosion gullies rapidly drain water from the forests, remove the subsoil and sedimentation as well as carry off logging debris. This result is regarded as the degradation of the landscape which causes flooding during intense precipitation.

All the negative aspects within the forested landscape increase the outflow of water from a territory and lead to its gradual dehydration. This process is the cause of flooding and loss of water in Slovakia and is applicable to many other countries and regions around the world. Such a country is akin to being diseased and requires treatment. Treatment consists of the revitalization of commercial forestry landscapes in order to restore the eco-system and reduce the risks of flooding and drought. Effective revitalization is focused on micro-basin restoration in elevated terrains situated above municipalities where the intensity of flood damages can be averted. Flooding intensity and frequency provides us with insights into what direction to look to in order to mitigate these anthropogenic processes. For centuries, man has been interfering in the natural processes of an ecosystem through intense landuse alterations, now we have something to learn from this and gain new experiences.

ELEMENTS CONTRIBUTING TO FLOOD RISKS

A large quantity of water that causes damage by volume and strength

Kinetic energy of water during intense precipitation carries soil, gravel, stones, wood and small debris causing clogging of bridges, streams and other water channels and gullies

Layers of humus and mud carried away from the forest by excess water run-off

EXAMPLES OF DAMAGED FORESTS

Two overused and unmaintained logging roads meet with a large erosion gully running through them.

Erosion gully forming on an unmaintained logging road.

A hiking trail turns into a stream during rain with no diversion throughs in place, water leaves the forest.

EXAMPLES OF ENVIRONMENTAL MAINTENANCE FROM THE PAST

Our ancestors, to the best of their knowledge, took care of the earth responsibly. In addition to the gentler processing of agricultural lands and a more sensitive approach to forestry, they maintained water balance by building various water retention measures such as brick check dams, wooden cascades, riffles, wooden catchment areas for fish, vegetative bank reinforcements of rivers and streams and other measures. In the Kysuce area situated in north central Slovakia, we have found a number of such old structures, especially wooden ones, which serve their purpose of water retention for decades to this day. According to the description by the locals, the oldest wooden dam - approx. 2 m high - is located in the village of Radôstka, in the Hulák district. This relatively large check dam was built in the 1950’s and is still functioning without any required maintenance.

Wooden check dam in the village of Radôstka,

Hulák district was built in the 1950’s and still

Functions to this day.

Wooden cascade in the village of Vysoka

nad Kysucou built in the 1940’s.

Wooden cascades in the village of Vysoká nad Kysucou have been protecting the bridge downstream against flood waves since its inception. Fish catchments built decades ago for trout breeding are scattered throughout the Kysuce area and have survived large floods.

IMPLEMENTED WATER RETENTION MEASURES

STONE CHECK DAMS

Oščadnica – Masonry stone dam with a capacity of 30,000m3 of water retention with an expected life expectancy of 100+ years

Krivany – dispersed stone check dam

Lačnovský potok – Dispersed stone check dam

Stara Bystrica - masonry stone dam with outflow pipe

Kriviansky potok – stone check dam

LAYERED CHECK DAMS

Vyšné Vane- layered check dam with a membrane

Nová Bystrica- Check dam with Willow weaving

Krasňany – layered check dam

Krasňany – layered check dam

Dunajov – Check dam slowing snow melt in the spring

Hlohovec – check dam in eroded gully

Check dam after heavier rainfall

Stará Bystrica – check dam made of Willows

RAINWATER DIVERSION THROUGHS

Nová Bystrica – rainwater diversion trough on logging road

Krivany – rainwater diversion trough

Dunajov – construction of a diversion trough on a logging road

CASCADES

Krasňany – Wooden cascade check dams

Krivany – palisade with membrane

Dunajov – combined check dam made of stone and wood

Palisade check dam with membrane

Simple palisade check dam

During heavy rainfall, run-off is slowed down

SMALL RESERVOIRS

Hranovica – small catchment reservoir built above a Roma settlement

Reservoir comprised of a wooden check dam at its edge

Nižné Vane - reservoir for forest fire fighting built along a forest road

Stará Bystrica – small retention reservoir for peak flow control

Hlohovec – check dam made of wood and stones

Diversion throughs, seepage pits and soaking belts are also a key part of the revitalization of micro-territories. Most of these measures use wood as their main structural element.

Retention Swale

Retention swale with infiltration pit

STABILITY AND DURABILITY OF CHECK DAMS AND OTHER RETENTION MEASURES

The main element of a stable and durable check dam is its proper construction. The transverse wooden logs should be layered with branches and pulp (fascines) along the profile of the corridor. It is important to reinforce the edges of the logs and fascines with stones and soil to ensure their stability.

Another important static element is the embedding of cross-cuts in between the transverse logs and fascines on the slope spanning a height of 1 to 1.5 m within the space between the dam walls. This space should not exceed the combined diameter of the logs used so that these cross cuts are firmly in place (20-30 cm).

The entire transverse and cross-sectional structure is stabilized by wooden steaks 8-12 cm in diameter which are hammered into the bed of the corridor until they cannot be wedged. These three elements are interconnected by nails of appropriate size. If using coniferous timber, then it is vital to remove the bark from the logs and steaks.

The stability and strength of the check dam is augmented after a first rainfall because sedimentation settles in and around the structure and loose space is filled in.

Assuming the inaccessibility of the terrain, all work is done manually. By the check dam, the cross-sectional logs are not inserted into excavated grooves but are secured on the slope. Fascines are secured using copper wire 2-3 mm in thickness.

CONSIDERATIONS FOR DESIGN AND IMPLEMENTATION OF CHECK DAMS

Synergy with forestry and agricultural landscape

Placement of check dam in the narrowest profile of the corridor and directly against the current while simultaneously ensuring that the retention area achieve its maximum size

Individual check dams should not affect the effectiveness of other individual check dams

Co-operation with stream managers and landowners is absolutely essential

It is necessary to take into full consideration the historical value and uses of the water basin